Process for the fibrous esterification of cellulose



Patented May 7, i935 g 2 0 02 r UN E T S PATENT OFF!CE, 1 PROCESS 'FORL-THE' 'FIBROUS ESTERIFICA- I I V TI ON-OFCELLULOSE v e V 7 Carl J. and Charles Rochester, i V v N.-Y., assignors to Eastman Kodak Company, j

Rochester, N. Y., a corporation ot New York H No bre i g; Ap plication February a osz,

Thepresentinvention relates to the fibrous the other-hand; are much less toxic and have s esterification of cellulose in whichan ether" lower vapor pressures than the' commonly ein-J' havinga boiling point higher than 7 0310., is ployedznon-"solvents so that any danger of the employed as a non-solvent or diluent in {the poisoning of -wjorkmen is reduced to a 5: esterification bath. by carrying-cut theesterification process ac- 5 Processes for the esterification of cellulose cording toQur inVentiOnL v I may be broadly divided intc the two classes of 7 Rather readily -hydrolyzed, 1 carbon tetrachlo- (1) the dope-forming and (2) the fibrous or ride has always had a moreorless corrosive acnon-dope-forming types. At "the present time tion on metals with which it contacted. This 10 v the *firstclass of processes are employed almost danger is eliminated :by our invention-as far as 10. to the exclusion of "the second. This lack of the corro'sion' of metal by the non-solvent eme use of fibrous cellulose esterification processes ployed inthe fibrous 'es terification of cellulose maybe partly duejto the fact thatthe'estrs is concerned as thehigher ethers =have' no prepared by the dope-forming'process'es as a chemical actionias -i'ar as can be determined,

i rule exhibit better qualities such as better staon the metals commonly employed for the re 15 bility to heat and detrioratiori'than thepro'd action vessels which cellulose esterification' ucts usually prepared by fibrous esterification processes are performed; processes. However the preparation ofcellulose "The-use 'of an ethyl" ether or isopropyl ether esters by dope-forming "processesfinvolves the each of which have/boiling pointsbelow '70 -C.,

- additional step of precipitation after the; esterias non-solvents' inthe fibrous esterification of ,20 fic'ation (and in some cases an additional cellulose ma'y efveii besuggested, however we hydrolysis treatment has taken place) but have found that 'the'se compounds are not suit-- fibrous esterification processes, on the other able foruseas noi i-solvents or diluents in-the hand, such a step is entirely unnecessary. It' esterificati'on of cellulose due to their extremev may thus be seen that'aprocess for the fibrous volatility resulting inmuch waste of non-solvent, 25

esterificationtof 'celluloseiis mostdesirab1e,1pro-. inflammability" -and the general difficulties 'invicling' a cellulose ester may be preparedby that herent' in their handling. Consequently a1-- process which is comparable to that prepared though ethyl ether has'long beenknownandhas by the dope-forming processes now employed been employed as a precipitant for cellulose 30, By our present invention, particularly when es'tei's'other non-solvents such'as benzeneand perchloric acid which isv soluble" in the'higher carbon tetrachloride have been commonly-emboiling ethers is employed as acatalyst, a celluploy-ed in the-processes for'the fibrous 'esterifica-' lose ester is producedwhaving good: stability tion' of cellulose; Although isopropyl ether which ester may be employed in.the various less 'volatile and moreea'sily handled thanethyl capacities in which cellulose esterswprepared by ether whenit is employed-asanon-solvent in the 35 dope-forming processes. are now employed as fibrous est-erification of cellulose it appears to y will be more fully pointed out hereinafter. 5 act as abuffer for the 'catalystand a decelerant The non-solvents commonly employed at-thej of thereaction'when' compared'with the ethers present time in reaction mixtures for the fibrousboiling above'70*C. For: example cellulose was 40 esterification of'cellulose are'henzene and 1car-v completely ester-ified in 12-hours in a fibrous 4o bon'tetrachloride.v The high boiling ethers howesterification bathin whicha higherboiling ether ever exhibit a solvent action lower than-that wasusedas the diluent and in which either per of benzene and carbon tetrachloride especially chloric acidor sulfuric acid could be used as the in the case of theymixed and-"higher esters of catalyst." However when'the sameesterification is cellulose and consequently these ethers are are: Wasattempted 'eXceptthat isopropylether was quired in much less amounts than 'eitherbenemployed as the diluentgit'was found that the zene or carbontetrachloride to "obtain the same esteriflcatio'npf thecellulose was only partially non-solvent effect inthe preparation ofifibrous completed eveniafter -a much longer period of esterification baths. Also benzene and carbon esterification. -V;ii r tetrachloride .due to, vtheir. toxity have .;.a de- .gThe above "facts :with regard .to lower boiling 50. cidedly detrimental physiological-efiect on'the ethers such as ethyl and isopropyl/ethers would human system when :either of them are/em seemto indicate that: the higher boiling ethers l y diin s ff nt quantities so, that the: suit-1 would be even less suitablejor use as non-solrounding air becomes'contaminated Withkfihell vents in fibrous esterification baths as it is Vamrs- The higher ethers which eemmoy; on usually the case that thelower m mbers of a higher boiling ethers are more suitable for use as diluents in those baths bon tetrachloride.

One object of our invention is to provide a ti e n ne or fibrous esterification process for preparing cel-v lulose esters in the presence of a 'higherboiling ether which does not decelerate the esterification and which is easily handled Another object of our invention is to provide a process for the fibrous esterification of cellulose in whichperchloric acid maybe employed as a'catalyst, thereby avoiding the dangerof; introducing sulfate groups into.,the. cellulose.- Another object of our invention is to provide afibrousprocess for preparing fullyv esterified cellulose esters in which a non-solvent is employed which is less, harmful to the operationof the process than those now commonly .used and which has no corrosive actionon the metal of which the re action vessels are made;

We have found that cellulose may be esterifled up to and includingv thepoint of complete esterification in a reaction mixture in whichan ether having a boiling pointabove 70 C., is employed. We have'found that ,the conventional reaction mixtures for the esterification of cellulose con--. tainingan organic acid anhydrid and a small amount of catalyst may be employed in con-- junction with a higher, boiling ether for the fibrous esterification of cellulose,

We have found thatby ourinvention due to the eflicacy of the non-solvents which ,we employ, less quantities of non-solvent are necessary than are commonly employed in fibrousesterification processes. We have found,. ,that theesters pre-. pared according to our invention are at-least, equal to and as a rule superior; to the cellulose esters prepared by other fibrous esterification processes. In our process when sulfuric acid is used as a catalyst, it is usually employed in small amounts as the higher ethers which we'use have no buffering effect, on the catalyst making an excess amount of catalyst unnecessary, so that any danger from combined sulfur in the cellu-. lose ester formedis reduced to ,a minimum which.

, is not the case where an appreciable amount of sulfuric acid is present in the reaction, bath.

However when perchloric acid or some other non-sulfuric catalyst is employed in an esterification process according, to our invention the danger of any sulfation ofthe: cellulose ester formed is completely eliminated.

E-f mr 50 lbs. of cotton linters was allowed to stand in a mixture of 300 lbs. of glacial acetic acid, 150 lbs. of normal propyl ether (b. p. 89) and 4 lbs. of a mixture of 3 parts of phosphoric and 1 part of sulfuric acid, for about 4 hours at 80 F. 150 lbs. of acetic anhydrid (85%) containing slightly less than a pound of sulfuric acid was then added and the whole was maintained at a temperature of 100 F. for 12 hours. The

fibrous cellulose acetate formed was separated from its reaction bath, was washed with n-propyl ether until all acid was removed and was then dried. It was found to be soluble in chloroformalcohol which indicates a completely acetylated cellulose.

Example II .The same procedure was followed as in the preceding example except that propionic acid was employed instead of the acetic acid in the 1 pretreatment in that example. A cellulose acetate-propionate was obtained which was soluble inv solvents such as acetone, ethylene chloride etc. without the need of hydrolysis, making possible the'formation of films, filaments, etc. from an unhydrolyzed ester of cellulose.

Example III 50 lbs. of cotton linters was pretreated with a mixture of 300 lbs. of butyric acid, 150 lbs. of normal butyl ether (b. p. 142 C.) and 5 ounces of 70% perchloric acid for 4 hours at 80 F. A mixture of 150 lbs. of acetic anhydrid (85%) Emample IV 50 lbs. of cotton linters was pretreated with a mixture of 300 lbs. of acetic acid, 150 lbs. of normal propyl ether and 5 ounces of perchloric acid (70%) for 4 hours at 80F. A mixture of 150 lbs. of 85% acetic anhydrid and 8 ounces of perchloric acid (70%) was then added to the mass and the whole was maintained at 100 F. for 18 hours. A cellulose acetate was formed which showed much greater stability vto heat than a fibrous cellulose acetate prepared in the customary manner.

As pointed out above, the ethers having a boiling point above 70 C., especially the aliphatic ethers, may be employed as the nonsolvent in the esterification of cellulose. Some of theethers. which we have found particularly suitable are the n-propyl, n-butyl, iso-butyl, iso-amyl and n-amyl ethers.

It is an important feature of our invention that the esterification processes in accordance therewitlr may be carried. out in the presence of only a relatively small amount of catalyst. We have found that processes in which an appreciable amount of catalyst such as sulfuric acid is employed result in aproduct of little if any value. The large amount of catalyst in such processes apparently has a marked de-. grading action on the cellulose which may even result in the conversion of the cellulose to a cellobiose or some other compound resulting from the degradation of'cellulose.

1 judgment of the individual operator.

Cotton linters is specified as the starting material in the examples as, due to its economy and satisfactory susceptibility to esterification, it is usually employed in the preparation of cellulose esters at the present time, however other cellulosic materials may also be employed in this connection. For example such materials as cotton fiber tissue paper, clean cotton, sur-' gical cotton wool (preferably bleached) and carefully prepared sulfite wood pulp which has been bleached may be employed as the starting material. Also easily esterifiable cellulosic materials such as so-called hydrocellulose, reverted cellulose such as may be derived from the viscose or cuprammonium process and even cellulose nitrates, acetates, formates or ethers, which con-" tain free hydroxyl groups available for esterification by processes carried out according to our invention, are also suitable as the starting material of our process of preparing cellulose esters. The term cellulosic materia as employed herein refers to materials comprising either celluluose none of whose hydroxyl groups have been replaced or cellulose which has been partially esterified or etherified but which still contains free and esterifiable hydroxyl groups. For example a cellulose acetate-propionate may be formed by employing as a starting material a cellulose acetate which has been hydrolyzed down to an acetyl content of say about 35-39%,

in a propionation bath such as one in which propionic acid and propionicanhydrid would be employed together with a higher boiling I ether according tov our invention.

The various conditions for carrying out the esterification of cellulose according to our invention may be varied in accordance with the For example the selection of temperatures, proportions, catalysts, time of treatment, etc. is merely a matter of technique and any such variations are possible in processes within the scope of our invention. Various other modifications such as the employment of various anhydrides and acids are apparent to those skilled in the art. For

- example a substituted fatty acid anhydrid such as a chloracetic anhydride or an alkoxyacet'ic (such as methoxyor ethoxy-acetic) anhydride as disclosed in Clarke and Malm application Serial No. 179,177, now Patent No. 1,880,808, Oct. 4, 1932 may be employed instead of or supplementary to the unsubstituted anhydrides and/or substituted fatty acids such as chloracetic or alkoxyacetic acid may be employed instead of or supplementary to the unsubstituted acids providing only that a source of acyl groups be present in the reaction mixture.

What we hereby claim as our invention and desire to secure by Letters Patent of the United States is:

1. The fibrous esterification of cellulosic material in a bath containing as a catalyst, perchloric acid and a sufllcient amount of an aliphatic ether having a boiling point above 70 C. to prevent solution of the ester formed therein.

2. A process of preparing a cellulose ester in fibrous form which comprises reacting upon the cellulose in a bath containing acetic'anhydrid, an organic acid and an aliphatic ether having a boiling point above 70 C. V

3. A process of preparing a cellulose ester in fibrous form which comprises reacting upon the cellulose in an esterifying bath containing an aliphatic ether having a boiling point above 4. A process of preparing a cellulose ester in fibrous form'which comprises reacting upon the cellulose in an esterifying bath containing as a catalyst, perchloric acid and an aliphatic ether having a boiling point above 70 C.

7. The fibrous esterification of cellulose in a bath containing a sufiicient amount of normal butyl ether to prevent solution of the ester formed therein.

8. The fibrous esterification of cellulose in a bath containing a suflicient amount of iso-amyl ether to prevent solution of the ester formed therein. 9. A process of preparing a cellulose ester in fibrous form in an esterifying bath containing acetic anhydride, an organic acid, perchloric acid as a catalyst and an aliphatic ether having a boiling point above 70 C.

10. A process of preparing cellulose acetate in fibrous form in an esterifying bath containing acetic anhydride, acetic acid, perchloric acid as a catalyst, and an aliphatic ether having a boil- CARL J. MALM. CHARLES L. FLETCHER. 

